Spectroscopy system and method for performing spectroscopy

Abstract

A spectroscopic system is disclosed that includes a resonant cavity, a first conduit configured to connect at a first end to a gas source and at a second end to a first end of an adsorption tube containing a sample for analysis, and a second conduit configured to connect at a first end to a second end of the adsorption tube and to connect at a second end to the resonant cavity.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 62 / 828,750, filed April 3, 2019, the contents of which are incorporated herein by reference in their entirety.

[0002] FIELD OF THE DISCLOSURE This disclosure relates generally to gas sample analysis, and more particularly to spectroscopy systems and methods for performing spectroscopy. [Background technology]

[0003] Spectroscopic systems analyze the interactions between matter and radiation to learn about matter. Typically, this analysis is used to classify materials or constituents according to previous baseline observations of known molecules. One such form of spectroscopy is Cavity Ring-Down Spectroscopy ("CRDS"), which is typically used to identify and quantify single analytes in a sample using their absorption spectrum. A typical CRDS system uses a laser that generates a beam that is directed into a cavity in a chamber that has two highly reflective mirrors. The beam is usually in the visible or near infrared ("IR") spectrum and is tuned to a single wavelength to identify the presence of a single molecule. The beam is then repeatedly reflected between the mirrors, which allows a portion of the light to escape the ring-down cavity. When the laser is resonant with a cavity mode, the intensity increases in the cavity due to constructive interference. When the light entering the cavity is extinguished, the intensity of the light in the ring-down cavity decays at a given rate. A small fraction of the light is not reflected by the mirror and escapes the ring-down cavity, and the intensity of the escaping light is measured by a sensor component to determine the attenuation rate.

[0004] When a gas sample is placed in the ring-down cavity, analytes present in the gas sample absorb a portion of the light, thereby accelerating the decay of the light intensity in the ring-down cavity. An absorption spectrum is generated by measuring the decay time of light at a number of specific wavelengths in the presence of the gas sample versus the decay time of light in the absence of the gas sample at those wavelengths. Linear regression of the measured absorption spectrum for the gas sample with the known absorption spectra of various analytes, or other suitable methods, allows for the identification and quantification of individual analytes in the gas sample.

[0005] Loading the sample can be problematic. Conventional techniques for loading the sample include connecting a bag made of plastic or other material to the CRDS system for analysis of the gas sample contained in the CRDS system. When the sample is of human breath, the sample contains CO2, which may interfere with the spectroscopy of other substances due to the molecular absorption characteristics of other substances contained in the breath sample. 2 and water. This is especially true when lasers having wavelengths in the infrared spectrum are used, since water absorbs light in this wavelength range. Additionally, CO 2 CO 2 It absorbs light at the wavelength emitted by the laser.

[0006] Another problem is that parts of the construction material can adhere to the inner surfaces of the spectroscopic system and can flake off during subsequent loading of samples, contaminating those samples. Summary of the Invention [Means for solving the problem]

[0007] In one embodiment, a spectroscopy system is provided that includes a resonant cavity, a first conduit configured to connect at a first end to a gas source and at a second end to a first end of a collection medium containing a sample for analysis, and a second conduit configured to connect at the first end to the second end of the collection medium and to connect at the second end to the resonant cavity. The resonant cavity can be a ring-down cavity.

[0008] The collection medium can be an adsorption tube. A heater can be positioned to heat the adsorption tube when the adsorption tube is connected to the first conduit and the second conduit.

[0009] The first end of the sorbent tube can be an exhaust end and the second end of the sorbent tube can be a sample receiving end.

[0010] The gas source can provide gas at a source gas pressure above a target sample pressure in the resonant cavity for analysis of the sample.

[0011] The spectroscopic system may further comprise a pressure sensor positioned upstream of the adsorption tube as gas flows from the adsorption tube to the resonant cavity.

[0012] The spectroscopic system may further include a control system coupled to the pressure sensor to receive the measured pressure from the pressure sensor and coupled to a valve that controls fluid communication between the gas source and the adsorption tube and the pressure sensor, the control system being configurable into a sample fill mode in which the valve is repeatedly opened and closed to introduce more gas from the gas source until the measured pressure becomes the target sample pressure.

[0013] The measured pressure can be compared to a target sample pressure when the valve is closed.

[0014] The valve can be a first valve, and the spectroscopic system may further include a second valve positioned along the second conduit, a third conduit in fluid communication with the first conduit and in fluid communication with the second conduit at a location between the second valve and the adsorption tube, a third valve controlling fluid communication through the third conduit, a fourth conduit in fluid communication with the first conduit between the first valve and the adsorption tube, and a fourth valve positioned along the first conduit between the third conduit and the fourth conduit.

[0015] A pressure sensor may be positioned along the third conduit between the first conduit and the third valve.

[0016] The spectroscopy system may further include a fifth valve positioned along the second conduit between the third conduit and the adsorption tube.

[0017] The spectroscopy system may further include a sixth valve positioned along the first conduit between the adsorption tube and the fourth conduit.

[0018] The control system may be configured to operate in a first mode in which the control system opens the first valve, the third valve, and the fifth valve and closes the second valve and the fourth valve to flow gas through the adsorption tube and the fourth conduit, and in a second mode in which the control system opens the first valve, the fourth valve, the second valve, and the fifth valve and closes the third valve to flow gas through the adsorption tube to the resonating cavity.

[0019] The spectroscopic system may further include a filter positioned along the second conduit.

[0020] In another aspect, a method of performing spectroscopy is provided that includes coupling a gas source to a first end of a collection medium containing a sample for analysis, coupling a second end of the collection medium to a resonant cavity, and flowing gas from the gas source through the collection medium to the resonant cavity, which may be a ring-down cavity.

[0021] The recovery medium may be an adsorption tube. The method may include heating the adsorption tube to a target temperature.

[0022] The first end of the sorbent tube can be an exhaust end and the second end of the sorbent tube can be a sample receiving end.

[0023] The method may further include measuring the pressure in the resonating cavity via a pressure sensor positioned upstream of the adsorbent tube as the gas flows from the adsorbent tube to the resonating cavity.

[0024] The method may further include repeatedly opening and closing a valve controlling fluid communication between the gas source and the sorbent tube until the measured pressure matches the target sample pressure level.

[0025] The measured pressure can be compared to a target sample pressure level when the valve is closed.

[0026] The flowing gas may include gas flowing through the adsorption tube from a first end of the adsorption tube to a second, sample receiving end of the adsorption tube, and the method may further include flowing gas through the adsorption tube from the sample receiving end to the exhaust end.

[0027] The method may include filtering the flowing gas before it enters the resonant cavity.

[0028] In a further aspect, there is provided a spectroscopy system comprising a resonant cavity defined by at least one internal surface and having a first mirror positioned towards a first end thereof and a second mirror positioned towards a second end thereof, wherein the at least one internal surface is inactive. The resonant cavity may be a ring-down cavity.

[0029] The spectroscopy system may further comprise a sample filling system coupled to the resonant cavity and having at least one conduit extending between a sample source and the resonant cavity, the conduit having an inert coating on an interior surface thereof.

[0030] The spectroscopy system may further include a sample filling system coupled to the resonant cavity and having at least one conduit extending between the resonant cavity and the exhaust outlet, the at least one conduit having a valve positioned therealong, and a portion of the at least one conduit extending between the resonant cavity and the valve having an inert coating on its interior surface.

[0031] The spectroscopic system may further comprise a filter positioned to filter the gas before it enters the resonant cavity.

[0032] Other technical advantages may become readily apparent to one of ordinary skill in the art after review of the following figures and description.

[0033] For a better understanding of the embodiments described herein, and to show more clearly how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings in which: [Brief description of the drawings]

[0034] [Figure 1] FIG. 2 is a schematic diagram of various optical and pneumatic components of a cavity ring-down spectroscopy system according to one embodiment. [Diagram 2] 2 is a flow diagram of a general method of performing spectroscopy using the system of FIG. 1. [Figure 3A] FIG. 2 is a schematic diagram of a portion of the pneumatic components shown in FIG. 1 with the flow of nitrogen gas indicated during filling / evacuating the ring-down cavity. [Figure 3B] FIG. 2 is a schematic diagram of a portion of the pneumatic components shown in FIG. 1, with the flow of nitrogen gas indicated during release of water and / or carbon dioxide. [Figure 3C] FIG. 2 is a schematic diagram of a portion of the pneumatic components shown in FIG. 1, with the flow of nitrogen gas indicated during loading of the sample from the sorbent tube. [Figure 4A] FIG. 2 is a cross-sectional view of region F4A of the pneumatic components of the cavity ring-down spectroscopy system of FIG. 1. [Figure 4B] FIG. 2 is a cross-sectional view of an exhaust conduit between the ring-down cavity and a cavity outlet valve of the pneumatic component of the cavity ring-down spectroscopy system of FIG. 1. [Figure 4C] 2 is a cross-sectional view of a portion of the ring-down chamber of the CRDS system of FIG. 1, in which an inert coating is disposed on an interior surface of the ring-down chamber that defines the ring-down cavity. [Diagram 5] FIG. 2 is a schematic diagram of an electrical control system for controlling the various optical and pneumatic components of the cavity ring-down spectroscopy system shown in FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Unless explicitly noted otherwise, items depicted in the drawings are not necessarily drawn to scale.

[0036] For brevity and clarity of illustration, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or similar elements. Additionally, numerous specific details have been set forth to provide a thorough understanding of the embodiments described herein. However, it will be understood by those skilled in the art that the embodiments described herein may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the embodiments described herein. Although exemplary embodiments are shown in the figures and described below, it should be understood at the outset that the principles of the present disclosure may be implemented using any number of techniques, whether currently known or not. The present disclosure should not be limited in any way to the exemplary implementations and techniques shown in the figures and described below.

[0037] Various terms used throughout this description may be read and understood as follows, unless the context dictates otherwise: "or" as used throughout is inclusive as if written "and / or", singular items and pronouns as used throughout include their plural forms and vice versa, and likewise, pronouns of a gender include pronouns of their opposite, such that pronouns should not be understood as limiting what is described herein to the use, performance, or practice of one gender, and "exemplary" should be understood as "illustrating" or "using an example," and not necessarily as "preferred" over other embodiments. Further definitions of terms may be set forth herein, which may apply to previous and subsequent examples of those terms, as understood from reading this description.

[0038] Modifications, additions, or omissions may be made to the systems, devices, and methods described herein without departing from the scope of the disclosure. For example, system and device components may be integrated or separated. Furthermore, the operations of the systems and devices disclosed herein may be performed by more, fewer, or other components, and the methods described may include more, fewer, or other steps. Also, steps may be performed in any suitable order. As used herein, "each" refers to each member of a set, or each member of a subset of a set.

[0039] Any module, unit, component, server, computer, terminal, engine, or device illustrated herein that executes instructions may include or have access to a computer readable medium, such as a storage medium, computer storage medium, or data storage device (removable and / or non-removable), for example, a magnetic disk, optical disk, or tape. Computer storage media may include volatile, non-volatile, removable, and non-removable media implemented in any method or technology for storage of information, such as computer readable instructions, data structures, program modules, or other data. Examples of computer storage media include RAM, ROM, EEPROM, flash memory, other memory technologies, CD-ROM, digital versatile disks (DVDs), other optical storage devices, magnetic cassettes, magnetic tapes, magnetic disk storage devices, other magnetic storage devices, or any other medium that can be used to store the desired information and that can be accessed by an application, a module, or both. Any such computer storage media may be part of the device or may be accessible or connectable to the device. Further, unless the context clearly dictates otherwise, any processing device or controller described herein may be implemented as a single processing device or as multiple processing devices. Multiple processing devices may be collocated or distributed, and any processing function referred to herein may be performed by one or more processing devices, even though a single processing device may be exemplified. Any method, application, or module described herein may be implemented using computer readable / executable instructions that may be stored or otherwise carried by such computer readable media and executed by one or more processing devices.

[0040] Various components of a spectroscopy system according to a particular embodiment are shown in Figure 1. In this embodiment, the spectroscopy system is a cavity ring-down spectroscopy ("CRDS") system 20, but may be any other suitable spectroscopy system, such as an electron spectroscopy system, an atomic spectroscopy system, etc.2 Laser 24 and Carbon-13 O 2 A laser 28 is provided. 2 Laser 24 and Carbon-13 O 2 Laser 28 is a gas-filled tube laser emitting at a series of pseudo-uniformly spaced, well-known frequencies that can be quickly selected using an adjustable diffraction grating device. Gas-filled tube laser technology has a long history and is a stable and robust method of generating infrared radiation at precisely known frequencies. 2 Laser 24 and Carbon-13 O 2 Both lasers 28 emit light in the mid-infrared spectrum.

[0041] CO 2 Laser 24 and Carbon-13 O 2 Each of the lasers 28 has one or more piezoelectrics that move the output coupler to allow adjustment of the length of the laser cavity, and an actuator to change the angle of the grating after the cavity, and thereby the pitch of the grating to adjust which wavelengths it reflects. By both adjusting the length of the laser cavity and changing the angle of the grating, the laser can be tuned very precisely to a particular wavelength and desired mode quality.

[0042] CO 2 The laser 24 generates a first laser beam 32, which is a carbon-13 O 2 Laser 28 generates a second laser beam 36. Depending on the optical frequency desired, 2 The laser 24 is adjusted to generate a first laser beam 32 while the carbon-13 O 2 The laser 28 is detuned or the carbon-13 O 2 The laser 28 is adjusted to generate a second laser beam 36 while the CO 2 Either the laser 24 is detuned. In this approach, a maximum of CO 2 Laser 24 and Carbon-13 O 2Only one of the lasers 28 outputs a beam at any particular time, so the first beam 32 and the second beam 36 are not combined simultaneously. Mid-infrared, specifically long wavelength infrared, was chosen as the type of light because most volatile organic compounds absorb light in this range. As a result, multiple volatile organic compounds can be measured by one system. CO 2 The laser operates in this range and has sufficient power and linewidth narrowness for ring-down spectroscopy. The use of two lasers increases the range and number of available wavelengths that the CRDS system 20 can use to analyze a gas sample.

[0043] The first laser beam 32 is redirected via a mirror 40 in the optical mount towards a beam splitter 44. The beam splitter 44 is partially reflective and partially transmissive and splits each of the first laser beam 32 and the second laser beam 36 into two beams: a sampling beam 48 and an actuation beam 52 that has the same properties as the sampling beam 48 and may be of similar intensity to the sampling beam 48.

[0044] The sampling beam 48 is received by a high speed infrared detector 56 which measures the amplitude and beat frequency of the sampling beam 48 using an oscilloscope. 2 Laser 24 or Carbon-13 O 2 This may indicate the presence of higher order modes resulting from less than optimal tuning of the laser 28. In response to detection of an undesirable beat frequency, the corresponding laser 24 or 28 is adjusted until the amplitude of the beat frequency is minimized or eliminated while maximizing intensity. If the amplitude of the beat frequency cannot be reduced below an acceptable level, the laser may be tuned to a different wavelength.

[0045] The actuation beam 52 continues to a first optical modulator 60, which deflects the actuation beam 52 to a mirror 64 in the optical mount. The mirror 64 redirects the light to a second optical modulator 68, which further deflects the actuation beam 52 to a focusing lens 72. The optical modulators are used to control the intensity of the light beam generated by the laser. In the embodiment here, the first optical modulator 60 and the second optical modulator 68 are acousto-optic modulators ("AOMs"), also referred to as Bragg cells. An AOM is a type of optical modulator that uses a piezoelectric transducer coupled to a material such as germanium or glass. In the embodiment described, the material is germanium. When an oscillating electrical signal is applied to the piezoelectric transducer, the piezoelectric transducer vibrates and creates sound waves in the material. These sound waves expand and compress the material, thereby creating periodic oscillations in the refractive index, allowing for Bragg diffraction. Light entering an AOM at the first Bragg angle relative to a plane perpendicular to the axis of propagation of the sound wave will be deflected by an amount equal to twice the Bragg angle at maximum efficiency. Eliminating the electrical signal removes the Bragg diffraction property of the material, allowing the light to pass undeviated, effectively attenuating the light along the deflected path. A by-product of the AOM is that the deflected light is shifted in frequency.

[0046] In other embodiments, the optical modulator may alternatively be an electro-optical modulator. An electro-optical modulator is another type of optical modulator that applies a DC or low frequency electric field to a material to distort the position, orientation, and / or shape of the material's molecules. As a result, the refractive index is altered, changing the phase of the outgoing beam as a function of the applied field. By sending the beam through a polarizer, the phase modulation is converted to intensity modulation. Alternatively, a phase modulator can act as an intensity modulator when placed in a branch of an interferometer.

[0047] Additionally, although the CRDS system 20 is described as having two optical modulators, in other embodiments the CRDS system may have a fewer or greater number of optical modulators.

[0048] The first optical modulator 60 and the second optical modulator 68 act as attenuators to adjust the intensity of the actuation beam 52 and extinguish the beam at the beginning of a ring-down event. A ring-down event involves extinguishing the actuation beam 52 illuminating the ring-down cavity or detuning the laser for the ring-down chamber and collecting light intensity data from the ring-down chamber. The first optical modulator 60 and the second optical modulator 68 are AOMs and therefore use the acousto-optic effect to diffract light using sound waves (usually at high frequencies). In each of the first and second optical modulators, a piezoelectric transducer is coupled to a material such as germanium or glass and an oscillating electrical signal is used to vibrate the piezoelectric transducer. The vibrating piezoelectric transducer expands and compresses the material, thereby creating periodic oscillations in the refractive index and creating sound waves in the material that enable Bragg diffraction. Light entering the AOM at a Bragg angle relative to a plane perpendicular to the axis of propagation of the sound wave will be deflected by an amount equal to twice the Bragg angle at maximum efficiency. Eliminating the electrical signal removes the Bragg diffraction property of the material, allowing the light to pass undeviated and effectively extinguishing the light along the deflected path. Thus, the intensity of the sound can be used to modulate the intensity of the light in the deflected beam.

[0049] The intensity of the light deflected by each of the first and second optical modulators 60 and 68 can be between about 85%, which represents the maximum deflection efficiency of the optical modulators 60, 68, and the attenuation limit of each of the first and second optical modulators 60 and 68, which is about 0.1% or less of the input light intensity. When the acoustic wave applied to the germanium is turned off, the deflected beam loses about 30 dB or more than 99.9% of its previous intensity. The attenuation limit represents an upper limit of how much the input light intensity can be reduced by the optical modulator.

[0050] The optical modulator is asymmetric in that, as a side effect, it Doppler shifts the frequency of the light in a first mode when the input light is accepted at a first end, and Doppler shifts the frequency of the light in a second mode opposite to the first mode when the input light is accepted at a second end and has the same attenuation power. However, the Doppler shift in the frequency of the light is in the same direction whether the light enters at the first end or the second end.

[0051] Conventional CRDS systems use a single optical modulator, resulting in an operating beam that is frequency shifted. These frequency shifts are generally small relative to the frequency of the light and can change the way the light is absorbed by the material in the cavity, but this frequency shift can be corrected during analysis. If the diffraction is toward the source of the AOM, the frequency shift is downwards, and if the diffraction is away from the source, the frequency shift is upwards. As discussed above, the effect is minimal.

[0052] The actuation beam 52 deflected by the second optical modulator 68 is focused via a focusing lens 72. The laser beam, and therefore the actuation beam 52, is 2 Laser 24 or Carbon-13 O 2 It continues to diverge as it travels from laser 28. Focusing lens 72 focuses the actuation beam 52 back to its original focus.

[0053] A mirror 76 on the optical mount then redirects the actuation beam 52 towards the ring-down chamber 80. The two mirrors 64, 76 extend the length of the path of the actuation beam 52.

[0054] The ring-down chamber 80 is an elongated tube that defines a resonant cavity referred to as ring-down cavity 84. A pre-cavity mirror 88a and a post-cavity mirror 88b (alternatively referred to herein as cavity mirror 88) are positioned at the longitudinal ends of the ring-down cavity 84. The cavity mirror 88 is highly reflective to both light directed at the cavity mirror 88 from outside the ring-down cavity 84 and to light directed at the cavity mirror 88 within the ring-down cavity 84. As a result, a portion of the operating beam 52 is directed to the pre-cavity mirror 88a, approximately 0.1% passes through the pre-cavity mirror 88a and into the ring-down cavity 84, and a majority of the operating beam 52, approximately 99.9%, is reflected back towards mirror 76.

[0055] The cavity mirror 88 is mounted on a mirror mount 92 that is actuable to adjust the positioning and orientation of the cavity mirror 88. Specifically, the front cavity mirror 88a toward the front of the ring-down cavity 84 is mounted on a mirror mount 92 that is actuable via three mechanized micrometers 96a. The back cavity mirror 88b toward the rear of the ring-down cavity 84 is mounted on a mirror mount 92 that is actuable via three piezoelectric micrometers 96b that can be manually adjusted for optical alignment, or on a piezoelectric actuable mirror mount 92 that can be further adjusted with a piezoelectric driver. In alternative embodiments, the front cavity mirror 88a and the back cavity mirror 88b may be actuated by any suitable means, such as via piezoelectric micrometers, mechanical micrometers, or the like.

[0056] The angle of each of the cavity mirrors 88 can be varied so that the light beam is aligned sufficiently so that it does not stray as it enters the ring-down cavity 84. If one of the cavity mirrors 88 is angled, some of the light will be reflected off the side of the ring-down cavity 84, causing a loss of light intensity, especially higher order modes. The micrometers 96 can be simultaneously adjusted to change the length of the ring-down cavity 84 without affecting the angular alignment. This allows tuning of the ring-down cavity 84 so that it is resonant at the frequency of the light entering the ring-down cavity 84.

[0057] Focusing lens 72 focuses the laser light to the optical mode of ring-down cavity 84 so that the beam minimum is positioned at or very close to the beam minimum waist of ring-down cavity 84. The position of focusing lens 72 can be adjusted to match the optical mode of the range of laser wavelengths.

[0058] An optical sensor in the form of a liquid nitrogen cooled detector 100 is positioned behind the back cavity mirror 88b to receive the light that escapes through the back cavity mirror 88b. The liquid nitrogen cooled detector 100 measures the intensity of the light that escapes from the ring-down cavity 84. Other types of sensors for measuring the intensity of the escaping light may be used in place of the liquid nitrogen cooled detector 100.

[0059] The sample is loaded from the sorbent tube into the ring-down cavity 84. The sorbent tube is the collection medium for the gases and vapors to be sampled. The sorbent tube is typically made from glass or stainless steel and can contain various types of solid sorbent materials ("sorbents"). Typical sorbents can include activated charcoal, silica gel, and organic porous polymers. The sorbent in the sorbent tube can be selected based on its ability to capture the compound of interest and not react with the compound of interest, thereby allowing the captured compound to be desorbed for analysis. In this embodiment, the sorbent tube is a thermal desorption tube 104 used to collect gas samples for testing. Thermal desorption tubes are generally made from stainless steel and contain various types of solid sorbent materials. Heat can be used to free the captured compound of interest from the sorbent in the thermal desorption tube. The sorbent tube is intended to be used with collection in one direction and desorption in the opposite direction. The sorbent material is typically more concentrated toward the sample receiving end of the sorbent tube. Also, some adsorbent tubes have more than one adsorbent, in which case it may be desirable to have the different adsorbents in a particular order and to adsorb and desorb in a particular orientation of the adsorbent tube.

[0060] An advantage of the sorbent tube is that it can concentrate the sample. For example, if the sample is a breath sample, the sorbent tube can be designed so that the sample contains a higher concentration of a larger specific molecule of interest relative to other smaller molecules. By specifically designing to capture the larger molecules, the concentration of the larger molecules relative to the smaller molecules can be increased, thereby improving the analysis of the breath sample. The concentration feature of the CRDS system 20 is particularly advantageous when more than one analyte, particularly one known analyte, is analyzed in the sample. When the analysis of the sample is performed to analyze the spectrum as a whole, rather than analyzing only a portion of the spectrum for a specific analyte, it is desirable to filter out other constituents that may dominate or overwhelm the measured spectrum, reducing the accuracy of the results.

[0061] In other embodiments, other types of sorbent tubes and other collection media may be used.

[0062] In a specific example, the sample is a sample of human breath collected from a patient. During sample collection, the person breathes into the sample receiving end 108 of the thermal desorption tube 104 to capture molecules from the breath for testing, and a portion of the person's breath is expelled through the exhaust end 110 of the thermal desorption tube. The person's breath contains a variety of constituents, including carbon dioxide, oxygen, and water molecules, as well as other larger molecules. These larger molecules include the particular compound of interest that is generally captured closer to the sample receiving end 108, while smaller molecules such as carbon dioxide, oxygen, and water are either more evenly distributed, more concentrated toward the exhaust end, or pass straight through the adsorption tube. As a result, the compound of interest is more concentrated toward the sample receiving end 108 of the thermal desorption tube 104. In other applications, the sample can be collected through one or both ends 108, 110 of the thermal desorption tube 104.

[0063] A pneumatic sample loading system 112 is used to load sample from the thermal desorption tube 104 into the ring-down cavity 84 and evacuate the sample loading system 112 including the ring-down cavity 84. During sample loading, the sample loading system 112 fills the ring-down cavity 84 with the collected sample (i.e., to desorb the gas sample from the thermal desorption tube 104 and into the ring-down cavity 84 without introducing contaminants), brings the pressure in the ring-down cavity to a target sample pressure of 1 atmosphere, brings the temperature to 50 degrees Celsius, and seals the ring-down cavity 84. In this embodiment, the absorption spectra for the set of samples to which the measured absorption spectra are compared are determined at this pressure and temperature to ensure consistency between these parameters that may affect the results. However, in other embodiments, the target sample pressure and temperature may be fixed at other heights for known and measured absorption spectra. During sample evacuation, the sample loading system 112 clears the previously provided sample from the ring-down cavity 84 and the various conduits for guiding the sample from the thermal desorption tube 104 to the ring-down cavity 84 .

[0064] The sample loading system 112 has an inlet portion that includes a nitrogen gas source 116. In this embodiment, the gas source is a nitrogen gas source, but in other embodiments, the gas source can be any other source of suitable gas. The nitrogen gas source 116 is a supply of gas in the form of very clean nitrogen gas that is pressurized or capable of pressurizing nitrogen gas to at least above a pressure of 1 atmosphere. In this embodiment, the nitrogen gas source 116 has a source gas pressure of 5 psi above ambient pressure, but this may be varied so long as the compression is sufficient to pressurize the ring-down cavity 84 to a target sample pressure of 1 atmosphere, or some other selected atmospheric pressure at which the analysis will be performed. In the illustrated embodiment, the nitrogen gas source 116 is nitrogen gas evaporated from a liquid nitrogen container. The nitrogen gas source 116 is in fluid communication with a gas supply conduit 120, which is further in fluid communication with the thermal desorption tube 104. A gas inlet valve 124a is positioned along the gas inlet piping 120a of the gas supply conduit 120. An auxiliary gas inlet valve 124b allows for the connection of other gases, but is not normally used. Gas inlet valve 124a and auxiliary gas inlet valve 124b communicate with gas inlet line 120a, which is further connected to flow line 120b of gas supply conduit 120.

[0065] The thermal desorption tube 104 is positioned within a heater 132 that can heat the thermal desorption tube 104 to free the sample from the sorbent in the thermal desorption tube 104. The heater 132 may be positioned to heat the entire thermal desorption tube, or alternatively, may be positioned to heat only the portion of the thermal desorption tube in which the sorbent material is located. Although the sample receiving end 108 and exhaust end 110 of the thermal desorption tube 104 are shown extending from the heater 132 in FIG. 1, in other embodiments the heater 132 may cover most or all of the thermal desorption tube 104.

[0066] A routing valve 124e is positioned along the routing line 120b, which is in fluid communication with the tube exhaust line 120c of the gas supply conduit 120. The routing valve 124e allows or prevents direct access to the tube exhaust line 120c. The tube exhaust line 120c is in fluid communication with the exhaust end 110 of the thermal desorption tube 104. The tube exhaust line 120c includes a forward tube isolation valve 124f. Thus, the gas supply conduit 120 extends between the gas supply 116 and the thermal desorption tube 104.

[0067] A sample supply conduit 121 is in fluid communication with the sample receiving end 108 of the thermal desorption tube 104 and the ring-down cavity 84. A rear tube isolation valve 124g is positioned along the initial portion 121a of the sample supply conduit 121. A cavity inlet valve 124d is positioned along the secondary portion 121b of the sample supply conduit 121. A filter 130a is positioned along the secondary portion 121b of the sample supply conduit 121 before the cavity inlet valve 124d. Thus, the sample supply conduit 121 extends between the thermal desorption tube 104 and the ring-down cavity 84. The filter 130a inhibits the ingress of contaminants, such as aerosols, into the ring-down cavity 84, which may deposit on the cavity mirror 88 and interfere with reflections, be scattered by aerosol particles, or otherwise reduce the light intensity at the ring-down cavity.

[0068] A bypass conduit 122 is in fluid communication with the gas supply conduit 120 and the sample supply conduit 121. A pressure sensor 128 is positioned along the bypass conduit 122. A bypass conduit valve 124c is positioned along the bypass conduit 122 between the pressure sensor 128 and the sample supply conduit 121.

[0069] A line exhaust conduit 123 is in fluid communication with the line exhaust plumbing 120c of the gas supply conduit 120 between the routing valve 124e and the foreline isolation valve 124f. The line exhaust conduit 123 includes a sample exhaust valve 124h and a mass flow controller 136.

[0070] The sample filling system 112 also has an exhaust subsystem for exhausting sample and gas from the ring-down cavity 84. The exhaust subsystem includes an exhaust conduit 140 in fluid communication with the ring-down cavity 84. A cavity outlet valve 124i is positioned along the exhaust conduit 140. A pressure sensor 144 is positioned along the exhaust conduit 140 between the cavity outlet valve 124i and the vacuum shutoff valve 124j. A vacuum pump 148 is positioned along the exhaust conduit 140 and is spaced from the pressure sensor 144 by the vacuum shutoff valve 124j. The vacuum pump 148 provides an exhaust outlet for the sample filling system 112. A vacuum inlet valve 124k is positioned along a pump inlet piping 150 in fluid communication with the exhaust conduit 140 between the vacuum shutoff valve 124j and the vacuum pump 148. The opposite end of the pump inlet piping 150 beyond the vacuum inlet valve 124k is in fluid communication with the ambient air. A filter 130b is positioned in the pump suction line 150 between the vacuum suction valve 124k and the opposite end of the pump suction line 150 to prevent the ingress of contaminants in the pump suction line 150 that may interfere with the operation of the vacuum pump 148.

[0071] Valves 124a-124k may alternatively be referred to herein as valves 124.

[0072] Sample supply conduit 121, cavity inlet valve 124d, exhaust conduit 140, and cavity outlet valve 124i are shown coupled to ring-down cavity 84 at specific locations for convenience, although it will be understood that the locations at which conduits 121, 140 and valves 124d, 124i are coupled to ring-down cavity 84 may vary. In a preferred configuration, sample supply conduit 121 communicates with ring-down cavity 84 toward the end of ring-down cavity 84 adjacent front cavity mirror 88a, and exhaust conduit 140 communicates with ring-down cavity 84 toward the end of ring-down cavity 84 adjacent rear cavity mirror 88b.

[0073] Figure 2 illustrates a method of performing spectroscopy with the spectroscopy system of Figure 1, generally at 300. With reference to Figures 1 and 2, when a new sample is to be loaded into ring-down cavity 84, a thermal desorption tube 104 containing the new sample is coupled to sample loading system 112. Specifically, the adsorption tube is coupled to a gas source (310) and coupled to the resonant cavity (320). In the embodiment described, the adsorption tube is thermal desorption tube 104 and the resonant cavity is ring-down cavity 84. Thermal desorption tube 104 is removable and reconnectable to allow for a different thermal desorption tube containing a different sample to be loaded.

[0074] During the evacuation process, gas is caused to flow through the resonating cavity (330). The vacuum inlet valve 124k is opened and the vacuum pump 148 is started. The vacuum inlet valve 124k is then closed and the vacuum shutoff valve 124j, the cavity outlet valve 124i, the cavity inlet valve 124d, the bypass conduit valve 124c, and the path valve 124e are opened in sequence. The contents of the path and the piping along the ring-down cavity 84 are evacuated from the CRDS system 20 by the vacuum pump 148. The pressure sensor 144 allows for the determination of when the system is sufficiently evacuated, and in particular, when the pressure sensor 128 is isolated from the vacuum pump 148. When it is determined that the sample filling system 112 and the ring-down cavity 84 are sufficiently evacuated, these same open valves 124j, 124i, 124d, 124c, and 124e are closed in the reverse order. Then, during a nitrogen fill phase, valves 124a, 124c, 124d, 124i, and 124j are opened to allow nitrogen gas from nitrogen gas source 116 to fill tubing 120a, 122, and 121, as shown in FIG. 3A. As will be appreciated, exhaust conduit 140 shown in FIG. 1 is also filled with nitrogen gas. At the same time, routing valve 124e and rear line isolation valve 124g are in a closed state. Nitrogen gas is then purged using another exhaust phase. The nitrogen fill phase and the exhaust phase can be repeated as desired to clear the tubing. Thus, the CRDS system 20 is exhausted of the previously tested sample.

[0075] Gas is then flowed through the adsorption tube to sweep it away from the resonating cavity (340). Between loads of a new sample, the thermal desorption tube 104 is flushed to remove carbon dioxide and water from the thermal desorption tube 104 so that the amount of carbon dioxide and water loaded into the ring-down cavity 84 is minimized. To flush the thermal desorption tube 104, the gas inlet valve 124a, the bypass conduit valve 124c, the rear tube isolation valve 124g, the front tube isolation valve 124f, and the sample exhaust valve 124h are opened to provide a path for nitrogen gas to flush the thermal desorption tube 104 forward. At the same time, the routing valve 124e and the cavity inlet valve 124d are closed to direct the flow of nitrogen as shown in FIG. 3B. The thermal desorption tube 104 is selected to suppress the recovery of carbon dioxide and water with the gas sample, but typically there will still be some carbon dioxide and water in the thermal desorption tube 104.

[0076] 500 ml of nitrogen gas is passed through the thermal desorption tube 104 to drive off any remaining carbon dioxide and water from the original sample in the thermal desorption tube 104. The mass flow controller 136 allows the nitrogen gas and the entrained carbon dioxide and water to be released at a specific flow rate. In this configuration, this flow rate is 500 ml / min. All valves 124 are then closed.

[0077] Once the carbon dioxide and water have been removed from the thermal desorption tube 104, the sample loading system 112 is again evacuated using the same process discussed above to remove the nitrogen gas introduced in the sample loading system 112 piping.

[0078] Thus, the sample loading system 112 can remove as much carbon dioxide and water as possible from the sample in the thermal desorption tube 104 before the sample is loaded into the ring-down cavity 84. This is of particular interest because water and carbon dioxide absorb mid- and long-wave infrared wavelengths such as those that may be generated by the lasers 24, 28.

[0079] Next, a heater 132 surrounding the thermal desorption tube 104 heats 350 the thermal desorption tube 104 to a target temperature to thermally desorb the sample within the thermal desorption tube 104 .

[0080] Gas is flowed through the adsorption tube into the resonating cavity (360). Once the thermal desorption tube 104 is sufficiently warmed, the CRDS system 20 switches to a sample loading mode. To this end, the gas inlet valve 124a, the route valve 124e, the front tube isolation valve 124f, the back tube isolation valve 124g, and the cavity inlet valve 124d are opened to provide a direct path for nitrogen gas from the nitrogen gas source 116, through the thermal desorption tube 104 with the desorbed compound of interest, and into the ring-down cavity 84. At the same time, the bypass conduit valve 124c, the sample exhaust valve 124h, and the cavity outlet valve 124i are closed to force the nitrogen gas along the path as shown in FIG. 3C.

[0081] The pressure is then measured via the pressure sensor 370. Achieving a target sample pressure of 1 atmosphere in the ring-down cavity 84 is desirable as all of the reference data collected and analyzed is at this pressure height, thereby ensuring that the results are reproducible.

[0082] In the embodiment shown and described, the gas inlet valve 124a is toggled open and closed by the system. The system waits for pressure to equalize in the ring-down cavity 84 and in a conduit in fluid communication with the ring-down cavity 84 along which the pressure sensor 128 is located. The pressure sensor 128 is located upstream of the thermal desorption tube 104 when valves 124a, 124e, 124f, 124g, and 124d are opened and valves 124c and 124h are closed, thereby preventing contamination by the sample. As a result, it may take a short period of time for pressure to equalize between the ring-down cavity 84 and the pressure sensor 128, especially since the adsorption tube allows gas to pass through itself at a limited rate, thereby slowing the equalization process. In other embodiments, other types of valves, such as throttling valves, may be used.

[0083] It is then determined (380) whether the pressure is at the sample target pressure. Once pressure sensor 128 has stabilized, if the pressure reading is less than the target sample pressure of 1 atmosphere, gas inlet valve 124a is again toggled open and closed to repeat the process until, after equalization, the pressure reading on pressure sensor 128 is at or sufficiently close to the target sample pressure of 1 atmosphere. When pressure sensor 128 indicates that the pressure level in ring-down cavity 84 is at or sufficiently close to the target sample pressure, valves, specifically at least valves 124a and 124d, are closed.

[0084] Once the target sample pressure is achieved or substantially achieved, spectroscopic analysis is performed on the sample (390), as described below.

[0085] If it is desired to desorb at multiple temperatures, vacuum inlet valve 124k is opened, vacuum pump 148 is started, vacuum inlet valve 124k is closed again, and vacuum shutoff valve 124j and cavity exit valve 124i are opened in succession to evacuate the contents of ring-down cavity 84. Cavity exit valve 124i is then closed before the desorption process is repeated.

[0086] Complete evacuation is generally not performed between multiple desorptions because there is still some gas sample along the sample supply conduit 121 between the backpipe isolation valve 124g and the cavity inlet valve 124d that would otherwise be lost.

[0087] By pressurizing a fixed volume ring-down cavity containing a gas sample to a desired pressure level in this manner, the surface area within the ring-down cavity to which compounds adhere can be reduced compared to a variable volume ring-down cavity that can be used to increase the pressure within the cavity to a desired level.

[0088] Conduits 120, 121, 122, and 123, valve 124, and ring-down cavity 84 have interior surfaces that are inert. Referring again to Figure 1, an inert coating 86 is shown applied to the interior surfaces of ring-down cavity 84. Inert coating 86 may be made from any suitable inert material, such as a silica-based or quartz material.

[0089] 4A shows a portion of the sample loading system 112 where the sample supply conduit 121 meets the bypass conduit 122. The conduits 121, 122 have an inert coating 152 on their inner or internal surfaces. For example, the inert coating may be made from a silica-based material. Additionally, the inner surface of each of the valves 124 is inert. For example, the valves 124 may use an FKM such as Viton for sealing. In an alternative implementation, the valves may use copper compression rings or the like.

[0090] 4B shows a portion of the exhaust conduit 140 between the ring-down cavity 84 and the cavity exit valve 124i. The interior surfaces of the exhaust conduit 140 and the cavity exit valve 124i are coated with an inert coating 152, such as a silica-based material. The cavity exit valve 124i may use an FKM, such as Viton, for sealing. In alternative implementations, the valve may use copper compression rings or the like. It is desirable to reduce the likelihood of any molecules present in the exhaust conduit and cavity exit valve 124i adhering to the interior surfaces of these elements, as such molecules may potentially find their way back into the ring-down cavity 84.

[0091] 4C shows a portion of ring-down chamber 80 having an interior surface 87 that defines ring-down cavity 84. An inert coating 86 provides interior surface 87 of ring-down chamber 80.

[0092] The use of inert materials on the interior surfaces of the sample filling system 112 and the ring-down cavity 84 reduces the amount of sample remaining in the ring-down cavity 84, conduits 120, 121, 122, valves 124, etc. As a result, previously analyzed samples are less likely to adhere to surfaces within the sample filling system 112 and the ring-down cavity 84 and are therefore less likely to detach and be analyzed with subsequent samples, thereby contaminating the results of the subsequent samples.

[0093] 5 is a schematic diagram of an electronic control subsystem 200 for the various components of the also illustrated CRDS system 20. All lines represent electrical or electronic signals, arrows represent one-way communication, voltage settings, etc., and non-arrowed lines represent two-way communication.

[0094] A computer 204 including one or more processors acts as a control module controlling the functions of the various components shown in Figures 1 and 3A-3C. The computer 204 has one or more processors 205 and a storage device 206 that stores computer-executable instructions that, when executed by the processors 205, cause the processors 205 to direct the other components of the CRDS system 20 as described herein.

[0095] The pair of RF drivers 208 2 Laser 24 and Carbon-13 O 2An approximately 40 MHz signal is sent to power the laser 28. Each of the lasers 24, 28 is tuned using an output coupler and a diffraction grating. A grating actuator 212 actuates (rotates) the diffraction grating. Another actuator actuates (translates) the output coupler. Each output coupler is driven by a 1000V output coupler piezo 216. A two-channel high voltage amplifier 220 that powers the output coupler piezo 216 is adjustable between 0V and 1000V. The high voltage amplifier 220 is configured with an analog output signal from a data acquisition ("DAQ") card 224 in the computer 204. The DAQ produces an output between 0V and 10V, and the high voltage amplifier 220 amplifies the signal by a factor of 100 to produce a 0V to 1000V signal to power the output coupler piezo 216. Each grating actuator 212, which changes the angle about the grating, is driven by an actuator driver 228 which is commanded by the computer 204 via RS-232. Each grating actuator 212 is moved many millimeters and this movement is translated into the pitch angle of the lasers 24, 28.

[0096] Data signals from the pressure sensors 128, 144 of the sample filling system 112 are received via RS-232.

[0097] The high speed infrared detector 56 is connected to a small amplifier 232 and an oscilloscope 236 which can be used to read the amplitude and frequency of the beat signal used to tune the lasers 24,28.

[0098] The temperature controller 240 for the thermal desorption tube heater 132 is controlled by the computer 204 via RS-232. The tube heater 132 consists of a temperature sensor and a piece of aluminum with heating tape wrapped around the temperature sensor. The heating tape and temperature sensor are both connected to the temperature controller 240, which is a PID (proportional-integral-derivative) controller. The controller sets and reads the temperature back to the main computer 204 via RS-232.

[0099] A relay board 244 is connected to the computer 204 and is used to turn on and off each of the solenoid valves 124 and the vacuum pump 148 .

[0100] A three channel piezoelectric driver 248 drives a piezoelectric actuator 252 which actuates a micrometer 96b to adjust the length of the ring-down cavity 84. Each path has two components: communication through RS-232 to a piezoelectric driver and an analog input from the DAQ card 224. In other embodiments, more than one piezoelectric driver may be used.

[0101] Each optical modulator 60, 68 is driven by an RF driver 256 that sends a signal of approximately 40 MHz. Changing the frequency of the RF driver 256 changes the Bragg angle for a given optical wavelength, or changes the optical wavelength to which a given or fixed Bragg angle is matched. When the RF driver 256 is tuned to a particular frequency and set to full power, most (approximately 85%) of the operating beam 52 passes through. When adjusted to 80%, 70%, the optical modulator 60, 68 will be attenuated. When the RF driver 256 is set to zero, the optical modulator 60, 68 will be completely turned off. The frequency of the RF driver is set through components via RS232. Analog and digital components can set the amplitude and on / off state of the RF driver 256. Specifically, the DAQ card 224 sends signals to a timing circuit 260, which in turn generates the four necessary signals required to enable and set the amplitude of the RF driver. The timing circuit 260 can operate in a steady state condition or in a condition where the timing circuit 260 sets the four voltages to zero and causes a ring-down back to the previous voltage level after a predetermined amount of time.

[0102] There is a digital output (“DO”) from the DAQ card 224 that controls the timing circuit 260 via a digitizer 264 .

[0103] Computer 204 is a control system coupled to pressure sensor 128 to receive a measured pressure from pressure sensor 128 and to gas inlet valve 124a which controls fluid communication between gas source 116 and thermal desorption tube 104. Computer 204 is conditioned to a sample fill mode in which computer 204 controls gas inlet valve 124a to repeatedly open and close to introduce more gas from gas source 116 until the pressure measured by pressure sensor 128 is the target sample pressure.

[0104] 1, once the gas sample fills the ring-down cavity 84, one laser 24 or 28 is tuned to a particular wavelength and its light is directed through a first optical modulator 60, reflected by mirror 64, passed through a second optical modulator 68, focused by focusing lens 72, and reflected by mirror 76 into the ring-down chamber 80. The optical modulators 60, 68 provide some attenuation to the actuation beam 52 in order to modulate its intensity.

[0105] When the actuation beam 52 reaches the pre-cavity mirror 88a, a fraction, approximately 0.1%, penetrates the pre-cavity mirror 88a and enters the ring-down cavity 84. The majority of the actuation beam, approximately 99.9%, is initially reflected back along the same path to the actuation laser 24 or 28.

[0106] Initially, the ring-down cavity 84 is not illuminated. As light enters the ring-down cavity 84 and most of the light in the ring-down cavity 84 is reflected between the two cavity mirrors 88, the amount or power of light in the ring-down cavity 84 begins to increase as more light is introduced from the outside via the actuation beam 52. A certain portion of the light leaks past the cavity mirror 88. It takes a period of time for the ring-down cavity 84 to "fill up" with light, which can occur when the cavity length is equal to the adjacent resonance length of the ring-down cavity 84 for the tuned laser. At this point, there is an equilibrium between the incoming light and the leakage. Once this equilibrium is achieved, the laser 24, 28 is extinguished or stopped from entering the ring-down cavity 84 via the optical modulator 60, 68. In other embodiments, the laser can be detuned so that it is not resonant for the configured cavity length.

[0107] The timing circuit 260 simultaneously directs the first light modulator 60 and the second light modulator 68 to attenuate the light beam at or near the attenuation limits of the light modulators 60, 68 to reduce the intensity of the light beam from the first light modulator 60. In the CRDS system 20, by directing both light modulators 60, 68 to be turned off simultaneously, the amount of light deflected by the first light modulator 60 during a short length of time is significantly reduced by the second light modulator 68 as the second light modulator 68 is turned off.

[0108] The extinction of the laser light provided to the ring-down cavity 84 can initiate a ring-down event. The resonant laser light provided to the ring-down cavity 84 may be extinguished in other ways in alternative embodiments, for example, by detuning the laser.

[0109] During the ring-down event, computer 204 registers the light intensity data reported by the liquid nitrogen cooled detector 100 exiting the back end of ring-down cavity 84. The ring-down event lasts for approximately 10 microseconds in the present configuration, but may last for longer or shorter times in other embodiments. The light decay time is approximately 2 microseconds.

[0110] Approximately 100 microseconds after the ring-down event is triggered, the timing circuit 260 directs the optical modulators 60, 68 to again begin passing the actuation beam 52 into the ring-down cavity 84. It is then determined whether sufficient ring-down data has been collected. The CRDS system 20 is configured in this embodiment to collect data from 500 ring-down events. When data from 500 ring-down events has been captured, the computer 204 stops operation of the piezoelectric driver 248 and then determines the decay rate from the ring-down event data. Instead, if it is determined that more ring-down data is to be collected, the computer 204 continues to direct the piezoelectric driver 248 to actuate the rear cavity mirror 88b.

[0111] The process is repeated for multiple frequencies of light to generate an absorption spectrum for the sample. For example, CO 2 The light generated by the laser 24 provides an absorption coefficient for a range of frequencies. 2 A range of frequencies of light can be generated from a laser 28. In this manner, an absorption spectrum can be developed for the sample.

[0112] In the embodiment described above, the light sources are two lasers that generate light in the mid-infrared range, but it is understood that other light sources can be used. For example, lasers that generate light in the visible spectrum, or near-infrared lasers may be used. Furthermore, in some circumstances, the CRDS system may include only one laser, or three or more lasers to generate the actuation beam.

[0113] In the previously described embodiment, the collection medium is an adsorption tube, specifically a thermal desorption tube, although other types of collection media may be used, for example, a solid phase microextraction ("SPME") device may be used with the system.

[0114] An electro-optic modulator may be used instead of an acousto-optic modulator.

[0115] The acousto-optic modulator may be configured such that the frequency of the operating beam is shifted up or down. As long as the net frequency shift provided by the acousto-optic modulator shifts the frequency of the operating beam sufficiently away from the frequency of the laser-generated operating beam such that the reflected light is outside the bandwidth of the generated laser light, the amount of interference between the reflected light and the generated operating beam may be minimized.

[0116] In other embodiments, three or more optical modulators may be used in the CRDS system to provide additional extinction capability to more quickly extinguish the actuation beam at the onset of a ring-down event, and in yet further embodiments, only one optical modulator may be used.

[0117] One or more focusing lenses may be used in other embodiments and may be translated to allow repositioning of the lenses to allow mode matching of each wavelength of the lasers.

[0118] The same approach may be adopted for other types of resonant cavities, particularly optical resonant cavities.

[0119] Another type of event can be triggered when the cavity length approaches the resonant length of the cavity for a specifically selected wavelength.

[0120] Analysis of the gas sample may be carried out at pressure levels other than 1 atmosphere in other embodiments, and therefore the width of the absorption spectrum may vary.

[0121] Although certain advantages have been enumerated above, various embodiments may include some, all, or none of the enumerated advantages.

[0122] In the embodiment described above, the resonant cavity is a ring-down cavity, however, in other embodiments, other types of resonant cavities may be employed.

[0123] Those skilled in the art will appreciate that many more alternative implementations and variations are possible, and that the above examples are merely illustrative of one or more implementations, and therefore, the scope is only to be limited by the claims appended hereto. [Explanation of symbols]

[0124] 20 CRDS System 24 CO 2 Laser 28 Carbon-13 O 2 Laser 32 First Laser Beam 36 Second Laser Beam 40 mirror 44 Beam splitter 48 Sampling Beam 52 Output Beam 56 High-speed infrared detector 60 First optical modulator 64 Mirror 68 Second Optical Modulator 72 Focusing Lens 76 Mirror 80 Ring Down Room 84 Ring Down Cavity 86 Inert Coating 87 Internal surface 88 Cavity Mirror 88a Front cavity mirror 88b Rear cavity mirror 92 Mirror mounting section 96 micrometers 96a Mechanized Micrometer 96b Piezoelectric Micrometer 100 Liquid nitrogen cooled detector 104 Thermal desorption tube 108 Sample receiving end 110 Exhaust end 112 Sample filling system 116 Nitrogen Gas Source 120 Gas supply pipe 120a Gas intake pipe 120b Path piping 120c pipe exhaust piping 121 Sample supply conduit 121a initial part 121b Secondary part 122 Detour conduit 123 Exhaust pipe 124 Valve 124a Gas intake valve 124b Auxiliary gas intake valve 124c bypass conduit valve 124d Cavity Inlet Valve 124e Path valve 124f Forward Pipe Isolation Valve 124g Rear Tube Isolation Valve 124h Sample exhaust valve 124i Cavity Outlet Valve 124j Vacuum shutoff valve 124k Vacuum Intake Valve 128 Pressure Sensor 130a, 130b Filters 132 Heater 136 Mass flow controller 140 Discharge conduit 144 Pressure Sensor 148 Vacuum Pump 150 Pump suction pipe 152 Inert Coating 200 Electronic Control Subsystem 204 Computer 205 Processing equipment 206 Storage device 208 RF drive unit 212 Lattice Actuator 216 Output coupler piezoelectric 220 High Voltage Amplifier 224 DAQ Card 228 Actuator drive unit 232 Amplifier 236 Oscilloscope 240 Temperature Control Device 244 Relay board 248 3-channel piezoelectric actuator 252 Piezoelectric Actuator 256 RF driver 260 Timing Circuit 264 Digitizer 300 How to Conduct Spectroscopy 310 Connect the gas source to the adsorption tube 320 Connecting the adsorption tube to the resonating cavity 330 Flowing gas through a resonant cavity 340 Flow gas through the adsorption tube to displace it from the resonating cavity 350 Heat the adsorption tube to the target temperature 360 Gas flows through the adsorption tube into the resonating cavity 370 Measure pressure via pressure sensor 380 Is pressure at target sample pressure? 390 Spectroscopic analysis is performed on the filled samples

Claims

1. A resonant cavity; a gas supply conduit configured to connect at a first end to a gas source and at a second end to a first end of a collection medium containing a sample for analysis; a sample supply conduit configured to couple at a first end to a second end of the collection medium and to couple at a second end to the resonant cavity; a bypass conduit extending from the gas supply conduit to the sample supply conduit; a tube exhaust conduit extending from the gas supply conduit between the bypass conduit and the recovery medium to an outlet; a routing valve positioned along the gas supply conduit between the bypass conduit and the line exhaust conduit, the routing valve being conditionable to allow or prevent the flow of gas along the gas supply conduit from the gas source to the collection medium; a cavity inlet valve positioned along the sample supply conduit between the bypass conduit and the resonant cavity, the cavity inlet valve being conditionable to allow or block the flow of gas into the resonant cavity; a bypass conduit valve positioned along the bypass conduit and adjustable to allow or block the flow of gas through the bypass conduit toward the sample supply conduit; a sample exhaust valve positioned along the tube exhaust conduit, the sample exhaust valve being adjustable to allow or block gas flow toward the outlet distal to the sample exhaust valve; a control system configured to close the pathway valve and the cavity inlet valve in a collection medium flushing mode and open the bypass conduit valve and the sample exhaust valve so that gas flows from the gas source through the bypass conduit, through the collection medium, and through the tube exhaust conduit toward the outlet, and also configured to open the pathway valve and the cavity inlet valve in a sample filling mode and close the bypass conduit valve and the sample exhaust valve so that gas flows from the gas source, through the collection medium and the sample supply conduit, and into the resonant cavity; A spectroscopic system comprising:

2. The spectroscopy system of claim 1 , wherein the collection medium is an adsorption tube.

3. The spectroscopy system of claim 2 further comprising a heater positioned to heat the sorbent tube when the sorbent tube is coupled to the gas supply conduit and the sample supply conduit.

4. The spectroscopy system of claim 2 , wherein the first end of the adsorption tube is an exhaust end and the second end of the adsorption tube is a sample receiving end.

5. The spectroscopy system of claim 4 , wherein the gas source provides the gas at a source gas pressure above a target sample pressure in the resonant cavity for analysis of the sample.

6. The spectroscopy system of claim 5 further comprising a pressure sensor positioned upstream of the adsorbent tube as gas flows from the adsorbent tube to the resonant cavity.

7. 7. The spectroscopy system of claim 6, wherein the control system comprises a gas inlet valve positioned along the gas supply conduit between the gas source and the sample supply conduit and coupled to the pressure sensor to receive a measured pressure from the pressure sensor, and in the sample filling mode, the gas inlet valve is repeatedly opened and closed to introduce more of the gas from the gas source until the measured pressure becomes the target sample pressure.

8. The spectroscopy system of claim 7 , wherein the measured pressure is compared to the target sample pressure when the gas inlet valve is closed.

9. The spectroscopy system of claim 8 , wherein the pressure sensor is positioned along the bypass conduit between the gas supply conduit and the bypass conduit valve.

10. 10. The spectroscopy system of claim 9, further comprising a back-tube isolation valve positioned along the sample supply conduit between the bypass conduit and the adsorption tube.

11. The spectroscopy system of claim 10 further comprising a forward tube isolation valve positioned along the gas supply conduit between the adsorption tube and the tube exhaust conduit.

12. 11. The spectroscopy system of claim 10, wherein the control system is configured to, in a resonant cavity flushing mode, close the route valve and the backpipe isolation valve and open the cavity inlet valve and the bypass conduit valve to flow the gas through the bypass conduit to the resonant cavity.

13. 1. A method of performing spectroscopy, comprising: connecting a gas source to a first end of a collection medium containing a sample for analysis via a gas supply conduit; connecting a second end of the collection medium to a resonant cavity via a sample supply conduit, the sample supply conduit being connected by a bypass conduit to a gas supply conduit, the gas supply conduit being connected to an outlet via a tube exhaust conduit extending from the gas supply conduit between the bypass conduit and the collection medium, a pathway valve being positioned along the gas supply conduit between the bypass conduit and the tube exhaust conduit, the pathway valve being conditionable to allow or prevent gas flow from the gas source along the gas supply conduit to the collection medium, and a cavity inlet valve being connected to the bypass conduit. a bypass conduit valve positioned along the sample supply conduit between a bypass conduit and the resonant cavity, the cavity inlet valve being conditionable to allow or block the flow of gas into the resonant cavity, a bypass conduit valve positioned along the bypass conduit and conditionable to allow or block the flow of gas through the bypass conduit towards the sample supply conduit, and a sample exhaust valve positioned along the tube exhaust conduit and conditionable to allow or block the flow of gas towards the outlet located distal to the sample exhaust valve; closing the pathway valve and the cavity inlet valve and opening the bypass conduit valve and the sample exhaust valve in a collection medium flushing mode to allow gas to flow from the gas source through the collection medium toward the outlet; opening the pathway valve and the cavity inlet valve and closing the bypass conduit valve and the sample exhaust valve in a sample-fill mode to flow the gas from the gas source through the collection medium to the resonant cavity; The method includes:

14. The method of claim 13 , wherein the collection medium is an adsorption tube.

15. The method of claim 14 further comprising the step of heating the adsorption tube to a target temperature.

16. 16. The method of claim 15, wherein the first end of the sorbent tube is an exhaust end and the second end of the sorbent tube is a sample receiving end.

17. 17. The method of claim 16, further comprising measuring the pressure in the resonant cavity via a pressure sensor positioned upstream of the adsorbent tube as the gas flows from the adsorbent tube to the resonant cavity.

18. 18. The method of claim 17, further comprising the step of repeatedly allowing or preventing fluid communication between the gas source and the adsorption tube by opening and closing a gas inlet valve positioned along the gas supply conduit between the gas source and the sample supply conduit until the measured pressure corresponds to a target sample pressure level.

19. 20. The method of claim 18, wherein the measured pressure is compared to the target sample pressure level when the gas inlet valve is closed.

20. The method of claim 17 further comprising filtering the flowing gas before it enters the resonant cavity.

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